If you fill the cupcakes while they are still warm, the filling will melt and turn the cupcakes gooey. You can bake the cupcakes from scratch using your favorite recipe, or you can bake them using a boxed mix. Snip off the bottom of a piping bag first, then insert a decorating tip into the bag. A small, sound tip will work the best, but you can use a larger star-shaped tip as well. Smooth fillings, such as custard, puddings, buttercream frosting, or whipped cream will work the best. You can also try jam or jelly, but make sure that it's not the chunky kind, otherwise you might clog the tip. Push it into the cupcake by about 1 inch (2.54 centimeters). You do not need to cut a hole into the cupcake first. Depending on the size of the cupcake, you should be able to squeeze 1 to 2 tablespoons of filling into it. If the filling starts to leak outside of the hole, stop; you have filled the cupcake as much as possible. Use a piping bag and a large round or star shaped decorator's tip to pipe buttercream frosting onto the cupcake. You can also use chocolate ganache. Glace icing made from powdered sugar and water is not recommended, however; it is too thin and will sink into the hole.
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One-sentence summary -- Bake your cupcakes and let them cool completely. Insert a decorating tip into a piping bag. Fill the bag with 1 to 2 tablespoons of your desired filling. Insert the tip into the top of the cupcake. Squeeze the filling into the cupcake. Frost and decorate the cupcake as desired.


1 balloon Duct tape Cake plate A medium-small box (size of a cake) Icing (make sure it’s thick and opaque) Sprinkles Friend who likes cake Real cake to say you’re sorry (optional) You can use any type of box for this, but something the size of a medium-small cake (roughly 9 inches by 9 inches) would be perfect. You’ll also want to make sure that the sides are high enough to hold in an inflated balloon. A huge sheet-cake-sized box could also work but isn’t ideal, as it would just require more balloons and more icing. Inflate a balloon large enough that it fills the box as much as possible without distorting the sides of the box. Once the balloon is in the box, use some duct tape to secure it there — 1 strip of tape vertically and 1 horizontally should be fine, but you can use more if you think you need to.  You can also use painting tape or electrical tape if you don’t have duct tape. Just don’t use Scotch tape, as this will be too thin and not sticky enough to properly hold in the balloon. You want to use enough tape that the balloon sits firmly in the box and doesn’t move around when you touch it. You’ll want to do this before you begin icing the “cake” so that you don’t make a mess on your counter — also, it will be easier to transport once it’s iced. Use a spatula to cover the balloon and box with icing. You want to cover the entire thing so that it looks like a cake. Make sure the icing is thick and opaque — you don’t wan it to be runny or see-through, or it’ll be easier to tell what’s underneath it. Do whatever else you want to do to make the cake look extra tasty and alluring. You might even write your friend’s name on it with icing. Your friend will probably be pretty excited to get a cake. If it’s not their birthday, you’ll need to find some other convincing reason for offering them cake. For example, if you’re having a movie night, you could say that you were bored at home and felt like making some cake. If you do this, you can’t push them to eat it otherwise they might know something’s up. You’ll have to wait for them to want the cake and cut it. If your friend is excited about the cake, he/she will probably want it right away. Make sure he/she’s the one to cut it, but don’t act too obvious about wanting them too. You can just hand them the knife and say you’ll get plates. If your friend doesn’t seem to want the cake, you can ask them to cut you a slice, but this might be more obvious. If they go into the kitchen to get themselves a drink, you could say, “Hey do you mind cutting me a piece of that cake?” and then act like you’re busy on your phone. When your friend cuts the cake, he/she’ll likely scream when it pops loudly. This is when you laugh, and hopefully he/she will laugh too. Getting a balloon cake isn’t as funny as giving one. If you give someone a balloon cake, make it up to them by giving them a real one afterwards. At the very least, give them a cupcake!
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One-sentence summary --
Gather your materials: Cut the top off a box. Inflate a balloon. Place the balloon in the box and tape it in. Place the balloon-box on a cake plate. Ice the balloon and box. Add sprinkles and any other decorations. Give the cake to your friend. Have them cut the cake. Laugh hysterically. Apologize and give them a real cake (optional but recommended).